Hollow Nitrogen-Doped Carbon Spheres with Presiding Graphitic Nitrogen for Oxygen Reduction Reaction

Hollow nitrogen-doped carbons, a class of metal free electrocatalysts, offer a wide range of modifications due to their tunable diameter and carbon wall thickness. Herein, hollow nitrogen-doped carbon spheres (HNCS-1000) with numerous structural defects, thin carbon wall of about 8 nm, high (sp 2 -sp 3 )/sp 3 bond ratio of 3.11 and graphitic-N proportion of 71.4% are prepared using a double pyrolysis strategy. When employed as ORR catalyst in O 2 -saturated 0.1 M KOH solution, HNCS-1000 retains high onset and halfwave potentials of 1.03 V and 0.88 V, respectively. In addition, it also demonstrates excellent stability/durability with 90.25% current density retention after 84000 s continuous chronoamperometric operation and only 33 mV loss in halfwave potential after 7000 CV cycles. Overall, the ORR performance of HNCS-1000 surpasses most of the previously reported nitrogen-doped carbon catalysts, and it is among the best catalysts for ORR in alkaline environment.